Phase transfer catalyzed reaction of a dimetal dicarboxylate with a haloorganoalkoxysilane can be performed using a quaternary ammonium catalyst, such as benzyltrimethylammonium chloride. However, benzyltrimethylammonium chloride suffers from the drawback of being thermally unstable at temperatures used for this reaction, and thus would not be considered a high performance catalyst. Tetrabutylammonium halides, such as tetrabutylammonium bromide (TBAB), may also be thermally unstable at the temperatures needed to produce the bis(alkoxysilylorgano)dicarboxyl functional compounds. Using TBAB as a phase transfer catalyst may result in catalyst decomposition products, e.g., tributylamine and butylfumarate, being present in the product.
Amine quat salts suffer from being less thermally stable and less efficient (since they are decomposing under the conditions of the reaction) and can generate undesired by-products during the reaction and afterwards during recovery of the product, e.g., by elevated temperature distillation of the product away from the catalyst residue than phosphonium compounds. The decomposition by-products can be difficult to separate by distillation because of similarity of boiling point and because they are being continually generated during attempts at purification.
Phase transfer catalyzed reaction of a dimetal dicarboxylate with a haloorganoalkoxysilane with use of phosphonium salts such as Ph3PMeCl suffers from the drawback that the phosphonium salts used are more toxic than their ammonium counterparts.
A thermally stable, amine based phase transfer catalyst, hexaethylguanidinium chloride has also been disclosed. However, hexaethylguanidinium chloride is available as an aqueous solution that must be thoroughly dried before use, which is an undesirable additional, and energy consuming, process step. Hexaethylguanidinium chloride also suffers from the drawback of being difficult to obtain in commercial quantities.
There is a continuing need in the art to provide alternative phase transfer catalysts. Phase transfer catalysts suitable for use in nonaqueous environments are desired.